Mississippi Administrative Code
Title 11 - Mississippi Department of Environmental Quality
Part 5 - Underground Storage Tank Regulations
Chapter 2 - Mississippi Commission on Environmental Quality Underground Storage Tanks Regulations Technical Standards and Corrective Action Requirements for Owners and Operators of Underground Storage Tanks (UST) (Adopted March 22, 1989; Amended August 25, 2011, Last Amended August 23, 2018)
Appendix 11-5-2-280.1 - GUIDELINES FOR THE EVALUATION OF UNDERGROUND STORAGE TANK CATHODIC PROTECTION SYSTEMS
Appendix 11-5-2-280.1-B - GLOSSARY
100 mV POLARIZATION - One of the three criteria that are commonly accepted as indicating adequate cathodic protection has been achieved. It is typically measured by interrupting the protective current on an impressed current system. When the current is interrupted, an "instant off" potential is recorded and the structure under cathodic protection is then allowed to depolarize until a change of at least 100 mV in potential is observed. Not more than 24 hours should be allowed for the depolarization to occur when conducting this test.
850 ON - One of the three criteria that are commonly accepted as indicating adequate cathodic protection has been achieved. It is measured with the protective current applied and is typically the only measurement possible with galvanic systems since the anodes cannot be disconnected. This criterion is not applicable to impressed current systems since a large portion of the "on" measurement can be comprised of a voltage drop when the protective current is applied.
850 OFF - One of the three criteria that are commonly accepted as indicating adequate cathodic protection has been achieved. It is measured with the protective current interrupted (either the power is cut off to the rectifier or the sacrificial anodes are disconnected). This criterion is considered by most to be the best indicator that adequate cathodic protection has been provided.
ANODE - The electrode of an electrochemical cell where oxidation (corrosion) occurs. With respect to cathodic protection, it can be thought of as the place where electrons leave the surface of a metal. Common galvanic anodes are zinc and magnesium.
AMPERE (AMP) - The basic unit of current flow in an electric circuit. Amperage can be thought of as "gallons per minute" in a water system.
AS BUILT DRAWINGS - Drawings that show how a system was actually installed in the field. Sometimes, unforeseen factors prevent the installation of a system as it was intended in the design drawings and this is why it is important to have detailed and accurate "as built" drawings.
ATTENUATION - The protective effects of cathodic protection current diminish as you move away from the source of the protective current. To illustrate this, on an impressed current system where the ground bed is installed only on one side of the tank bed, the end of the tanks away from the ground bed will receive less protective current than the side of the tanks closest to the anodes. Attenuation of protective current applies to galvanic systems as well.
CATHODE - The electrode of an electrochemical cell where reduction (and no corrosion) occurs. With respect to cathodic protection, it can be thought of as the place where current enters the surface of a metal.
CATHODIC PROTECTION - The technique of causing the entire surface of a metallic structure to become a cathode with respect to its external environment (soil). This is accomplished by supplying an electric current sufficient to overcome the tendency of naturally occurring electrical currents to leave the metallic structure.
CATHODIC PROTECTION EVALUATION - The interpretation of whether or not a cathodic protection system is providing sufficient corrosion protection. An evaluation incorporates all cathodic protection testing, surveys, rectifier operation/output measurements, consideration of voltage drops, condition of dielectric coatings, continuity, bond integrity, circuit integrity and any other factors or site specific conditions that may have an influence on the operation and effectiveness of a cathodic protection system.
CATHODIC PROTECTION SURVEY - Refers to the process whereby all of the structure-to-soil measurements necessary to contribute to the final evaluation of a system are obtained.
CATHODIC PROTECTION TEST- Refers to the process whereby only a single structure-to-soil measurement is obtained.
CONTINUITY - As related to cathodic protection, continuity means that two metallic structures are electrically continuous. With impressed current systems all protected structures must be continuous and this is normally accomplished through the use of wires referred to as continuity bonds.
CORROSION - The deterioration of a material (usually a metal) caused by an electro-chemical reaction with its environment. Corrosion of metals involves the flow of electrons (current) between an anode and a cathode. Corrosion will occur where the electrons leave the surface of a metal.
CURRENT TEST -A method of temporarily creating an impressed current cathodic protection system on a galvanically protected structure so that it can be determined how much protective current is necessary in order to achieve adequate cathodic protection. This is normally done by connecting a 12-volt battery to the structure to be tested and to a temporary anode.
DIELECTRIC MATERIAL - A coating that does not conduct electricity. Various coatings are utilized and some examples are the "fusion-bonded epoxy" found on factory coated steel piping and coal tar epoxies commonly found on sti-P3 tanks.
DISTRIBUTED GROUND BED - Used to describe an anode configuration in which the anodes are more or less equally distributed around the metallic structure that is intended to be protected.
ELECTROLYTE - As related to UST cathodic protection systems, electrolyte refers to the soil and/or water surrounding the metallic structure that is under cathodic protection.
ELECTROMAGNETIC INTERFERENCE - As related to corrosion protection, it is an external electrical current that causes an error in a voltmeter measurement. Sources are commonly associated with high voltage AC power lines, radio frequency transmitters and airport radar systems.
FAIL-See Section 7.1.4.
FIELD INSTALLED - Refers to any impressed current system or sacrificial anode cathodic protection system that is installed at a pre-existing UST location or when sacrificial anodes are installed on new metallic pipe in the field. Any cathodic protection system except for those associated with unmodified sti-Pj tanks may be thought of as "field installed".
FINAL POTENTIAL (VOLTAGE) - The voltage that is observed at the end of the depolarization period associated with the measurement of "100 mV polarization". The final voltage must be at least 100 mV less than the "instant off' voltage in order to meet the 100 mV polarization criterion for adequate cathodic protection.
"FIXED CELL - MOVING GROUND" - A technique for measuring continuity in a UST system whereby the reference electrode is placed in the soil at a location remote from the UST system and is left undisturbed (fixed cell) while potentials are measured on various parts of the UST system (moving ground).
GALVANIC (SACRIFICIAL) ANODE - A metal of high electro-potential (see Appendix J) that is used to protect another metal. Zinc and magnesium are two metals that are commonly utilized in the protection of UST systems.
GALVANIC CATHODIC PROTECTION - A cathodic protection system that utilizes sacrificial anodes to provide the protective current. The anode will corrode (sacrifice itself) instead of the metal it is intended to protect. The anode provides a protective current (reverses the electron flow) because it has a higher electrochemical potential than the metal it is intended to protect. Galvanic systems are normally limited to the protection of well coated structures because they have a very low driving potential.
IMPRESSED CURRENT ANODE - A metal that is utilized to deliver the current from a rectifier to the soil in order to protect the intended metallic structure. Impressed current anodes are commonly made of graphite, high silicon cast iron and "mixed-metal oxides" because the metal must be highly resistant to corrosion in order to have an acceptably long life span.
IMPRESSED CURRENT CATHODIC PROTECTION - A cathodic protection system in which the protective current is supplied by an external source (rectifier). The level of protective current that is delivered to the structure is adjustable and is much higher than that associated with galvanic anodes. For this reason, impressed current systems are utilized on those UST systems that are uncoated or require a high amount of protective current.
INCONCLUSIVE - See Section 7.1.4.
INSTANT OFF POTENTIAL (VOLTAGE) - The voltage that is observed momentarily after the power to an impressed current cathodic protection system is interrupted. It is used as the base line from which to begin calculating a "100 mV polarization". The second number that appears after the current is interrupted is considered the proper value to represent the instant off potential.
ISOLATION - As related to cathodic protection, isolation means that two metallic structures are electrically discontinuous. With galvanic systems a protected structure must be electrically isolated and this is normally accomplished through the use of nylon bushings and dielectric unions.
LOCAL POTENTIAL (VOLTAGE) - The structure-to-soil potential of a metallic structure that is measured with the reference electrode placed in the soil immediately over the protected structure.
NACE INTERNATIONAL - Acronym for National Association of Corrosion Engineers International.
NATIVE POTENTIAL (VOLTAGE) - The structure-to-soil potential exhibited before any cathodic protection is applied.
ON POTENTIAL (VOLTAGE) - The structure-to-soil potential that is measured with the protective current applied.
PARALLEL CIRCUIT - Can be caused by the person conducting the test making contact with a metallic part of the test leads, or reference electrode when conducting structure-to-soil potential measurements. The creation of parallel paths must be avoided since inadvertent errors can be introduced.
PASS-See Section 7.1.4
PASSIVATION - When a metal undergoes passivation, an oxidation layer forms on the surface of the metal due to corrosion and can be defined as the loss of chemical reactivity. The oxidation layer acts as a coating and prevents or slows further corrosion of the metallic object since oxygen is prevented from reaching the underlying metal.
PHOTOVOLTAIC EFFECT - Sunlight striking the electrolyte solution in a copper-copper sulfate reference electrode can cause an error in the observed structure-to-soil potential and must be avoided.
"POINT-TO-POINT" - A technique for measuring continuity in a UST system whereby each lead of a voltmeter is connected to the two metallic structures of interest (negative lead to one structure and positive to the other). The voltage difference (if any) measured with the voltmeter connected in this manner indicates if continuity is present or not.
POLARIZATION - The change in the structure-to-soil potential of a metallic structure due to the application of a protective current. In this guidance document, polarization is considered to mean cathodic polarization - that is, the potential of the metal is shifted in the negative direction.
POLARIZED POTENTIAL - The structure-to-soil potential of a metallic structure that is observed after the protective current is applied and sufficient time has elapsed for the structure to completely polarize.
RAISED EARTH - Term used to describe the high voltage gradient found in the soil around an active impressed current or sacrificial anode. Placement of the reference electrode in proximity to an active anode will cause an abnormally high (more negative) structure-to-soil potential than would be present if the anode were not in close proximity.
RECTIFIER - A device utilized in impressed current systems that changes AC power to DC power.
REFERENCE ELECTRODE - Also referred to as a reference cell or a half-cell. A device whose electrochemical potential is constant that is used to measure the structure-to-soil potential of buried metallic structures. The potential that is observed on the buried metallic structure is relative to the potential of the reference electrode. The potential of a buried metallic structure would be zero if it were of the exact same composition as the reference electrode if all sources of measurement error were eliminated.
RESISTANCE - A measurement of the tendency of a substance to inhibit the flow of electrical current. Resistance in UST cathodic protection systems is generally meant to refer to the electrical properties of the backfill materials (soil).
REMOTE EARTH - The structure-to-soil potential of a metallic structure that is measured with the reference electrode placed in the soil at a point well away (remote) from the protected structure. Remote earth is generally thought of as at least 25 feet and not more than 100 feet away. Remote earth is established when the observed structure-to-soil potential does not significantly change no matter how far away the reference electrode is from the protected structure.
SACRIFICIAL ANODE - See Galvanic Anode.
SHIELDING - A structure that prevents or diverts an electrical current from reaching the desired location. Normally thought of as something that stops a reference electrode from being able to "see" the metallic structure that you trying to measure.
sti-P3 TANK - A steel tank manufactured to the standard created by the Steel Tank Institute that comes from the factory with a "pre-engineered" cathodic protection system. The "P3" means that the steel tank is protected in three ways: 1) A protective dielectric coating is factory applied; 2) Sacrificial anodes (normally zinc) are factory installed on the tanks and 3) dielectric bushings are installed to facilitate electrical isolation of the tank.
STRAY CURRENT - An electrical current that travels along an unintended path. Normally thought of as a current from some external source that enters a protected metallic structure at one point that then exits at another point. The point where the stray current exits the protected structure can be subject to intense corrosion and failure may rapidly occur.
STRUCTURE-TO-SOIL POTENTIAL - Also known as "pipe-to-soil potential' or "structure-to-electrolyte potential" - The difference in the potential of the surface of a buried metallic structure and the electrolyte (soil) that surrounds it with respect to a reference electrode in contact with the electrolyte (soil). Can be thought of as the voltage difference between a buried metallic structure and the soil that it is buried in.
VOLTAGE - The basic unit of force in an electric circuit. Voltage is equivalent to pounds per square inch in a water system.
VOLTAGE (IR) DROP - With respect to UST cathodic protection systems, voltage drops may be thought of as any voltage that causes an error in the observed structure-to-soil potential. Whenever a current is flowing through a resistance, a voltage drop is present and is part of the voltage measurement obtained.
